In the operation of certain earth moving and other construction vehicles, efficient use of the vehicle requires frequent reversal of direction. When a drive reversal is executed with the vehicle in motion, a severe strain or damage may be imposed on the driveline and additionally the sudden movement may be uncomfortable or even hazardous to the operator of the vehicle. Heretofore, control systems have been devised for automatically reducing the speed of the vehicle before allowing drive reversal to take place.
The Fauchere U.S. Pat. No. 3,381,770 discloses a reversing control system for a vehicle to prevent excessive shock loading of the driveline when the operator calls for vehicle reversal with the vehicle in motion. In this system, a manually initiated reversing signal causes actuation of the drive reverser when the vehicle speed is below predetermined value; however, if the speed is above that value, the reversing signal causes actuation of the brakes and actuation of the reverser is prevented until the speed is reduced below the predetermined level. The Faucher control system is a servo-mechanism which requires feedback devices for indicating the respective positions of the reverser actuator and the clutch to control the sequencing of the servo-actuated components. Thus, this system requires the installation of limit switches and relays in operative relation with the components of the driveline of the vehicle.
The James U.S. Pat. No. 3,913,700 discloses a reversing control system for protecting the driveline of a vehicle when the operator calls for reversing of vehicle direction. A manually initiated reversing signal when the vehicle is in motion causes the brake to be applied and the engine speed to be reduced to a preset level and then the transmission is reversed. The system of the James Patent utilizes switch contacts for speed sensing and switch contacts for indicating the position of the drive direction selector which are connected in circuit with plural contacts of a relay controlled by the switches. In this control circuit, the control current must flow through the speed sensing and direction indicating switches to the solenoid valve for the transmission reverser and for the brake and throttle control means.
It is also known in the prior art to utilize hydraulic control systems to prevent reverse shifting of a transmission until the vehicle speed is reduced to a predetermined value. Such systems are disclosed in the Shore U.S. Pat. No. 3,858,696, Pleir U.S. Pat. No. 3,910,389 and the White U.S. Pat. No. 4,090,414.
A general objective of the present invention is to provide a transmission reversing control system which avoids the difficulties and disadvantages of the prior art and affords ease of installation and reliability in operation.